Effect of thermal stresses on the phase transition temperature in a ferroelectric-dielectric nanocomposite

Nechaev, V. N.; Viskovatykh, A. V.

doi:10.1134/s1063783414100217

Cited by 8 publications

(5 citation statements)

References 11 publications

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“…Factors reducing T C include correlation effects at the place of contact between the ferroelectric inclusion and the nonpolar phase, as well as the depolarizing fields arising near the surface of the ferroelectric inclusions. The effect on the Curie point in ferroelectric composites of the correlation interactions of the polar inclusion with the matrix, mechanical stresses and the depolarizing fields of the bound charges at the boundary of the ferroelectric inclusions has evaluated theoretically [ 21 , 22 , 23 , 24 , 25 , 26 , 27 ]. However, the effects of screening were not taken into consideration in these studies.…”

Section: Introductionmentioning

confidence: 99%

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites

et al. 2018

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The temperature of the transition to the polar state in ferroelectric composites, representing spherical ferroelectric inclusions embedded in a dielectric matrix, under a depolarizing field effect is investigated. This temperature is determined both in the absence and presence of screening effects of the depolarizing field of the bound charges of spontaneous polarization at the inclusions surface. The absence case shows that the Curie point shift is determined by the ratio of the Curie constant of the ferroelectric inclusion to the permittivity of the matrix. Screening effects show that the transition temperature shift decreases through multiplying the value by a decreasing factor equal to the ratio of the screening length to the radius of the ferroelectric inclusion. Examples of the materials for the position of the Curie point on the temperature scale, largely determined by the tilting action of the depolarizing field and the compensating shielding effects, are given.

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Section: Introductionmentioning

confidence: 99%

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites

et al. 2018

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“…When the crystallite dimensions are much larger than the unit-cell size, the contribution to the total matrix effect, which is associated with short-range interfacial interactions, becomes less significant than the contribution of long-range mechanical and electric fields appearing inside the ferroelectric inclusion. The mechanical matrix effect, which involves the elastic three-dimensional (3D) clamping of ferroelectric inclusions and the generation of thermal stresses due to dissimilar thermal expansion of two contacting materials [5][6][7][8][9], should be especially important for ferroelectric nanocrystals surrounded by rigid dielectric matrices such as glasses. Such FE-DE nanocomposites have been fabricated in many laboratories by embedding ferroelectric substances into various porous dielectrics, including synthetic opals [10,11], silica glass [12,13], sodium borosilicate glass [14,15], and aluminum oxide [16].…”

Section: Introductionmentioning

confidence: 99%

Dielectric properties of ferroelectric nanocomposites: effects of thermal stresses and filler shape anisotropy

Nikitchenko

Azovtsev

Pertsev

2018

J. Phys.: Condens. Matter

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Ferroelectric nanocomposites are intriguing nonhomogeneous materials, which may have unusual phase states and specific physical properties useful for practical applications. Here we theoretically describe dielectric properties of nanocomposites comprising single-domain ferroelectric nanocrystals embedded into a linear dielectric medium. First, small-signal intrinsic permittivities of spheroidal PbTiO and BaTiO crystallites surrounded by an isotropic matrix with linear elastic properties are calculated with the aid of a nonlinear thermodynamic theory. It is shown that thermal stresses caused by differences in thermal expansion between the inclusions and the matrix may strongly influence the intrinsic permittivities of ferroelectric nanocrystals. Second, macroscopic dielectric responses of ferroelectric-dielectric composites are evaluated in the Maxwell Garnett approximation. For effective permittivities of such composites, generalized relations are derived, which allow for both the shape and dielectric anisotropies of ferroelectric nanocrystals. Numerical calculations of the effective permittivities are performed for composites comprising PbTiO and BaTiO nanocrystals embedded into representative dielectric matrices generating tensile (silica glass) or compressive (potassium silicate glass) thermal stresses inside ferroelectric inclusions. For nanocomposites involving randomly oriented and similarly aligned spheroidal inclusions, temperature dependences of the effective permittivities are determined with the account of phase transitions occurring in strained ferroelectric nanocrystals and suppression of their dielectric responses due to the depolarizing-field effect created by low-permittivity matrix. Our theoretical calculations show that effective permittivities of composites comprising needle-like or disc-shaped ferroelectric inclusions could strongly exceed the permittivity of the matrix. Most importantly, we predict that BaTiO-KO-SiO composites with such inclusions should exhibit a broad dielectric peak around the room temperature, which is associated with shifted structural transitions in strained BaTiO nanocrystals. The presented theory provides guidelines for the development of ferroelectric nanocomposites with enhanced dielectric responses, which could be suitable for applications in supercapacitors and other advanced electronic devices.

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“…When a ferroelectric inclusion is surrounded by a dissimilar rigid medium, it is subjected to three-dimensional (3D) elastic clamping by the matrix and experiences thermal stresses caused by different thermal expansion coefficients of two contacting materials. Theoretical studies predict that these elastic and thermo-mechanical effects could significantly modify phase transitions in nanocrystals of perovskite ferroelectrics and their polarization properties [19][20][21][22]. However, comprehensive theoretical description of the influence of elastic matrix on the phase states of ferroelectric inclusions is still lacking.…”

Section: Introductionmentioning

confidence: 99%

“…Indeed, thermal stresses were not taken into account neither in the study of the effect of matrix rigidity on ferroelectricity in a spherical BaTiO 3 inclusion [19] nor in the thermodynamic calculations performed for ellipsoidal BaTiO 3 , PbTiO 3 , and Pb(Zr 0.5 Ti 0.5 )O 3 nanocrystals surrounded by silica glass [22]. The role of thermal stresses was investigated with the aid of a simplified model, which neglects the influence of ferroelectric polarization on elastic strains in the inclusion-matrix system, and only a stress-induced shift of the Curie temperature has been predicted [21].…”

Section: Introductionmentioning

confidence: 99%

Phase diagrams of ferroelectric nanocrystals strained by an elastic matrix

Nikitchenko

Azovtsev

Pertsev

2017

J. Phys.: Condens. Matter

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Ferroelectric crystallites embedded into a dielectric matrix experience temperature-dependent elastic strains caused by differences in the thermal expansion of the crystallites and the matrix. Owing to the electrostriction, these lattice strains may affect polarization states of ferroelectric inclusions significantly, making them different from those of a stress-free bulk crystal. Here, using a nonlinear thermodynamic theory, we study the mechanical effect of elastic matrix on the phase states of embedded single-domain ferroelectric nanocrystals. Their equilibrium polarization states are determined by minimizing a special thermodynamic potential that describes the energetics of an ellipsoidal ferroelectric inclusion surrounded by a linear elastic medium. To demonstrate the stability ranges of such states for a given material combination, we construct a phase diagram, where the inclusion's shape anisotropy and temperature are used as two parameters. The 'shape-temperature' phase diagrams are calculated numerically for PbTiO and BaTiO nanocrystals embedded into representative dielectric matrices generating tensile (silica glass) or compressive (potassium silicate glass) thermal stresses inside ferroelectric inclusions. The developed phase maps demonstrate that the joint effect of thermal stresses and matrix-induced elastic clamping of ferroelectric inclusions gives rise to several important features in the polarization behavior of PbTiO and BaTiO nanocrystals. In particular, the Curie temperature displays a nonmonotonic variation with the ellipsoid's aspect ratio, being minimal for spherical inclusions. Furthermore, the diagrams show that the polarization orientation with respect to the ellipsoid's symmetry axis is controlled by the shape anisotropy and the sign of thermal stresses. Under certain conditions, the mechanical inclusion-matrix interaction qualitatively alters the evolution of ferroelectric states on cooling, inducing a structural transition in PbTiO nanocrystals and suppressing in BaTiO inclusions some transformations occurring in their bulk counterpart. The constructed phase maps open the possibility to calculate dielectric properties of strained PbTiO and BaTiO nanocrystals and ferroelectric nanocomposites comprising such crystallites.

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Effect of thermal stresses on the phase transition temperature in a ferroelectric-dielectric nanocomposite

Cited by 8 publications

References 11 publications

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites

Influence of Depolarizing Fields and Screening Effects on Phase Transitions in Ferroelectric Composites

Dielectric properties of ferroelectric nanocomposites: effects of thermal stresses and filler shape anisotropy

Phase diagrams of ferroelectric nanocrystals strained by an elastic matrix

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